Some say the law was carefully drafted to withstand legal scrutiny. . .
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The law requires police to check with federal authorities on a person's immigration status, if officers have stopped that person for some legitimate reason and come to suspect that he or she might be in the U.S. illegally. The heart of the law is this provision: "For any lawful contact made by a law enforcement official or a law enforcement agency…where reasonable suspicion exists that the person is an alien who is unlawfully present in the United States, a reasonable attempt shall be made, when practicable, to determine the immigration status of the person…"
Critics have focused on the term "reasonable suspicion" to suggest that the law would give police the power to pick anyone out of a crowd for any reason and force them to prove they are in the U.S. legally. Some foresee mass civil rights violations targeting Hispanics.
What fewer people have noticed is the phrase "lawful contact," which defines what must be going on before police even think about checking immigration status. "That means the officer is already engaged in some detention of an individual because he's violated some other law," says Kris Kobach, a University of Missouri Kansas City Law School professor who helped draft the measure. "The most likely context where this law would come into play is a traffic stop."
As far as "reasonable suspicion" is concerned, there is a great deal of case law dealing with the idea, but in immigration matters, it means a combination of circumstances that, taken together, cause the officer to suspect lawbreaking. It's not race -- Arizona's new law specifically says race and ethnicity cannot be the sole factors in determining a reasonable suspicion.
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http://www.washingtonexaminer.com/opinion/columns/Byron-York/A-carefully-crafted-immigration-law-in-Arizona-92136104.html